Nitrogen polarity superlattice coordinated regulation high two-dimensional electron gas concentration transistor and method

Abstract

The invention discloses a high-two-dimensional electron gas concentration transistor cooperatively regulated and controlled by nitrogen polarity superlattices and a method. The device comprises a substrate, a superlattice stress regulation and control layer, a stress relaxation layer, a barrier layer and a channel layer, through a periodic heterostructure design, directional transmission and storage of stress can be realized at a nanoscale, and while the carrier concentration of a channel layer is improved, the electron transport characteristic is optimized through a quantum confinement effect; compared with a single-layer barrier structure, the multi-interface characteristic of the superlattice can effectively inhibit dislocation propagation and improve the crystal quality; when the superlattice layer is combined with a nitrogen polar material, the superlattice layer not only can relieve the stress mismatch problem of nitrogen polar epitaxy, but also can compensate interface charge loss through periodic energy band engineering; under the synergistic effect, the carrier density of the device is remarkably improved on the premise of keeping relatively high mobility, and meanwhile, the influence of the surface state density on the dynamic performance is reduced; the invention provides a feasible path for developing high-frequency and high-power density semiconductor devices.

Description

Technical Field

[0001] The present invention relates to wide bandgap semiconductor technology, and in particular to a high two-dimensional electron gas concentration transistor coordinatedly regulated by a nitrogen polarity superlattice and a preparation method thereof. Background Art

[0002] Group III nitride semiconductors (such as gallium nitride and aluminum nitride) have important research value in the field of power electronics and radio frequency devices due to their wide bandgap characteristics. The high breakdown field strength characteristics of this type of material can support higher operating voltages, and its high electron saturation velocity is conducive to high-frequency operation, while its good thermal stability provides the basis for device reliability. Among them, the two-dimensional electron gas (2DEG) synergistically generated by the spontaneous polarization of the material and the piezoelectric effect is the key physical mechanism for realizing high-mobility devices. In recent years, nitrogen-polar (N-polar) materials have shown higher theoretical polarization charge density and heterojunction design flexibility because their polarization direction is opposite to that of traditional gallium-polar (Ga-polar), but their epitaxial growth faces technical challenges such as high crystal defect density and difficulty in controlling surface roughness.

[0003] Improving the performance of existing gallium nitride-based high electron mobility transistors (HEMTs) faces multiple constraints: First, while increasing the thickness of the barrier layer can increase carrier concentration, the polarization charge density has a theoretical limit due to lattice mismatch stress relaxation. Second, the introduction of a high-aluminum barrier layer can easily lead to a decrease in interface quality, causing a trade-off between mobility and carrier concentration. Third, the current collapse effect caused by surface state defects significantly affects the device's dynamic characteristics, while the traditional structure's insufficient thermal stress management capabilities limit its high-temperature operating stability. Furthermore, when device feature sizes are reduced to the submicron level, improvements in gate control efficiency and frequency response performance encounter physical bottlenecks. Summary of the Invention

[0004] In response to the above problems in the existing technology, the present invention proposes a high two-dimensional electron gas concentration transistor with coordinated regulation of polar superlattice and its preparation method, which eliminates the constraints of insufficient two-dimensional electron gas density on the existing technology and realizes a high-mobility and high-carrier concentration HEMT heterostructure. The device design based on nitrogen polarity is conducive to the realization of ohmic contact and device application.

[0005] One object of the present invention is to provide a method for preparing a high two-dimensional electron gas concentration transistor with coordinated regulation of polar superlattice.

[0006] The method for preparing a high two-dimensional electron gas concentration transistor with coordinated regulation of polar superlattice of the present invention comprises the following steps:

[0007] 1) Providing a substrate, wherein the substrate is a semiconductor epitaxial substrate;

[0008] 2) forming a superlattice stress regulation layer on the substrate, the superlattice stress regulation layer comprising a first material and a second material arranged alternately, the first material and the second material having the same number of layers, both of which are Group III-V elements, the Group V elements being the same but the Group III elements being different, and having different lattice constants; the difference in lattice constants between the first material and the second material results in a lattice mismatch, thereby generating in-plane compressive stress; and the magnitude of the compressive stress is regulated by adjusting the lattice mismatch;

[0009] 3) forming a stress relaxation layer on the superlattice stress regulation layer, wherein the material of the stress relaxation layer is the same as the second material of the superlattice stress regulation layer; the stress relaxation layer releases excess stress accumulated in the superlattice stress regulation layer through a dislocation bending mechanism, and the compressive stress effect of the superlattice stress regulation layer on the upper structure is mostly shielded by the stress relaxation layer. The stress relaxation layer reduces the compressive stress through relaxation and separates the superlattice stress regulation layer from the barrier layer to prevent longitudinal leakage current and mutual interference between the energy bands of the superlattice stress regulation layer and the barrier layer;

[0010] 4) forming a barrier layer on the stress relaxation layer, wherein the barrier layer is made of a ternary alloy of group III-V elements, the elements of which are consistent with those of the superlattice stress regulation layer, i.e., the two group III elements are the group III elements of the first material and the second material of the superlattice stress regulation layer respectively;

[0011] 5) forming a channel layer on the barrier layer, wherein the material of the channel layer is the same as the second material of the superlattice stress regulation layer;

[0012] 6) The barrier layer and the channel layer form a heterojunction. The lattice mismatch and polarization effect cause a large amount of uncompensated polarized charge to accumulate at the interface, inducing the formation of a high-concentration and high-mobility two-dimensional electron gas on the channel layer side. The channel layer acts as a low-defect, high-mobility conductive channel to achieve efficient electron transport.

[0013] 7) The concentration of the two-dimensional electron gas is regulated by the barrier layer and the stress relaxation layer;

[0014] The concentration of the two-dimensional electron gas introduced by the barrier layer is related to the spontaneous polarization and piezoelectric polarization charge density of the barrier layer. The spontaneous polarization charge density is related to the composition of the group III element of the first material contained in the barrier layer, and the piezoelectric polarization charge density is related to the thickness of the barrier layer.

[0015] The compressive stress of the superlattice stress control layer generates a built-in electric field at the interface between the barrier layer and the channel layer, causing the band structure to bend. The band bending leads to a change in the two-dimensional electron gas concentration. The change in the two-dimensional electron gas concentration caused by the superlattice stress control layer is related to the period number and piezoelectric polarization charge density of the superlattice stress control layer, and the piezoelectric polarization charge density of the superlattice stress control layer is related to the compressive stress of the superlattice stress control layer.

[0016] By adjusting the thickness of the barrier layer and the composition of the group III element of the first material, as well as adjusting the period number and compressive stress of the superlattice stress control layer, the concentration of the two-dimensional electron gas is regulated, thereby increasing the concentration of the two-dimensional electron gas without reducing the mobility.

[0017] Wherein, in step 1), the material of the substrate layer is sapphire, silicon carbide, silicon, aluminum nitride or gallium nitride.

[0018] The invention further includes a nucleation layer formed on the substrate layer to alleviate the lattice mismatch between the substrate and the superstructure and inhibit the formation of threading dislocations. The nucleation layer is made of the same material as the second material of the superlattice stress-regulating layer, namely, a III-V element, wherein the Group III element is B.

[0019] The buffer layer is formed on the nucleation layer. The material of the buffer layer is the same as the second material of the superlattice stress control layer, that is, it uses III-V group elements and the group III element contained is B element. It serves as a high-quality crystal template and provides a low defect density foundation for the subsequent superlattice layer. According to the Matthews-Blakeslee model, the critical thickness h of the buffer layer is c for:

[0020]

[0021] Wherein, b is the Burgers vector of the second material, and f is the lattice mismatch, which is obtained by looking up the table according to the type of material selected and is a fixed value related only to the material.

[0022] In step 2), the first material and the second material are nitride, oxide or arsenide. The Group III elements contained in the first material and the second material are respectively denoted as A element and B element.

[0023] The compressive stress σ induced by the first material in a single cycle A Satisfy the following formula:

[0024]

[0025] Among them, E B is the elastic modulus of the second material, ν B is the Poisson's ratio of the second material, Δa is the lattice mismatch between the first material and the second material, a B is the lattice constant of the second material. To maintain a high in-plane compressive stress and reduce the interface roughness between the first and second materials, and to prevent stress field interference between multi-period superlattices, within a single period, the compressive stress storage efficiency of the first material is ensured to be >90%, and stress field interference between multi-period superlattices is prevented. Within a single period, the thickness of the first and second materials is 1 to 10 atomic layers (3 nm).

[0026] In step 3), the relaxation R and the thickness t of the stress relaxation layer B The relationship between them satisfies:

[0027]

[0028] Where k is the stress relaxation coefficient; the thickness of the stress relaxation layer ranges from 50 to 200 nanometers. The stress relaxation layer adjusts the compressive stress exerted by the superlattice stress regulation layer on the structure above. A higher relaxation coefficient reduces the compressive stress, further regulating the compressive stress of the superlattice stress regulation layer. The stress relaxation layer is composed of Group III-V elements, with the Group III element being element B.

[0029] In step 4), the barrier layer's Group V element is consistent with the superlattice stress-modulating layer's Group V element, and the barrier layer's two Group III elements are element A and element B. The composition of the Group III element, element A, in the first material of the barrier layer is between 0.2 and 0.3 to balance the two-dimensional electron gas concentration and the heterojunction interface quality.

[0030] In step 5), the thickness of the channel layer is 10 nm to 70 nm.

[0031] In step 6), the two-dimensional electron gas is confined in a triangular potential well near the heterojunction interface between the barrier layer and the channel layer, and the electrons can only move freely in the two-dimensional plane, which makes the electron mobility in the GaN channel layer reach 1600 cm 2 / (V·s) or above.

[0032] In step 7), the thicker the barrier layer, the higher the piezoelectric charge density; the higher the content of group III elements in the first material, the higher the spontaneous polarization charge density, the higher the two-dimensional electron gas concentration, and the lower the mobility.

[0033] The two-dimensional electron gas concentration is the total polarization charge density ρ total Satisfy the following formula:

[0034]

[0035] in, is the spontaneous polarization charge density of the barrier layer, is the piezoelectric polarization charge density of the barrier layer, is the piezoelectric polarization charge density introduced into the superlattice stress control layer, N is the number of periods of the superlattice stress control layer, The piezoelectric polarization charge density introduced within a single period of the superlattice stress control layer is related to the compressive stress induced by the first material within the single period. The greater the compressive stress, the higher the piezoelectric polarization charge density introduced.

[0036] Another object of the present invention is to provide a high two-dimensional electron gas concentration transistor with coordinated regulation of polar superlattice.

[0037] The high two-dimensional electron gas concentration transistor with coordinated polar superlattice regulation of the present invention comprises: a substrate, a superlattice stress regulation layer, a stress relaxation layer, a barrier layer and a channel layer; wherein the substrate adopts a semiconductor epitaxial substrate; a superlattice stress regulation layer is formed on the substrate, and the superlattice stress regulation layer comprises a first material and a second material arranged alternately, the first material and the second material have the same number of layers, both materials adopt III-V group elements, the V group elements of the two are the same but the III group elements are different, and have different lattice constants; the different lattice constants of the first material and the second material lead to a lattice mismatch, thereby generating a surface The compressive stress in the superlattice stress control layer is controlled by adjusting the lattice mismatch; a stress relaxation layer is formed on the superlattice stress control layer, and the material of the stress relaxation layer is the same as the second material of the superlattice stress control layer; the stress relaxation layer releases the excess stress accumulated in the superlattice stress control layer through the dislocation bending mechanism, and the compressive stress of the superlattice stress control layer on the upper structure is mostly shielded by the stress relaxation layer; the relaxation degree is controlled by adjusting the thickness of the stress relaxation layer; a barrier layer is formed on the stress relaxation layer, and the material of the barrier layer is a ternary alloy of group III-V elements, and the elements are consistent with the elements of the superlattice stress control layer, that is, the two The three group III elements are respectively the group III elements of the first material and the second material of the superlattice stress regulation layer; a channel layer is formed on the barrier layer, and the material of the channel layer is the same as the second material of the superlattice stress regulation layer; the barrier layer and the channel layer form a heterojunction; the two-dimensional electron gas concentration is regulated by the barrier layer and the stress relaxation layer; the two-dimensional electron gas concentration introduced by the barrier layer is related to the spontaneous polarization and piezoelectric polarization charge density of the barrier layer, the spontaneous polarization charge density is related to the composition of the group III elements of the first material contained in the barrier layer, and the piezoelectric polarization charge density is related to the thickness of the barrier layer; the compressive stress of the superlattice stress regulation layer is A built-in electric field is generated at the interface between the barrier layer and the channel layer, causing the band structure to bend, and the band bending leads to a change in the two-dimensional electron gas concentration; the change in the two-dimensional electron gas concentration caused by the superlattice stress regulation layer is related to the period number and piezoelectric polarization charge density of the superlattice stress regulation layer, and the piezoelectric polarization charge density of the superlattice stress regulation layer is related to the compressive stress of the superlattice stress regulation layer; by adjusting the thickness of the barrier layer and the composition of the group III element of the first material contained therein, as well as adjusting the period number and compressive stress of the superlattice stress regulation layer, the two-dimensional electron gas concentration is regulated, thereby achieving an increase in the two-dimensional electron gas concentration without reducing the mobility.

[0038] Advantages of the present invention:

[0039] Through the design of periodic heterostructures, the present invention can achieve directional transmission and storage of stress at the nanoscale, while improving the carrier concentration in the channel layer and optimizing the electron transport characteristics through the quantum confinement effect; compared with the single-layer barrier structure, the multi-interface characteristics of the superlattice can effectively suppress dislocation propagation and improve crystal quality; when combined with nitrogen-polar materials, the superlattice layer can not only alleviate the stress mismatch problem of nitrogen-polar epitaxy, but its periodic performance band engineering can also compensate for interface charge loss; this synergistic effect enables the device to achieve a significant increase in carrier density while maintaining a high mobility, while reducing the impact of surface state density on dynamic performance; the present invention provides a feasible path for the development of high-frequency, high-power density semiconductor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A cross-sectional view of an embodiment of a high two-dimensional electron gas concentration transistor coordinated by polar superlattice control according to the present invention;

[0041] Figure 2 This is an atomic force microscope image after pre-processing obtained according to an embodiment of the method for preparing a high two-dimensional electron gas concentration transistor with coordinated regulation of polar superlattice according to the present invention;

[0042] Figure 3 This is an atomic force microscope image of the buffer layer surface obtained according to an embodiment of the method for preparing a high two-dimensional electron gas concentration transistor with coordinated regulation of polar superlattice according to the present invention;

[0043] Figure 4 High-resolution transmission electron microscopy images of a superlattice stress layer obtained according to an embodiment of the method for preparing a high two-dimensional electron gas concentration transistor using cooperative regulation of polar superlattices of the present invention, wherein (a) is a high-resolution transmission electron microscopy image of AlN:GaN=3:7, (b) is a high-resolution transmission electron microscopy image of AlN:GaN=4:2, and (c) is a high-resolution transmission electron microscopy image of AlN:GaN=2:2;

[0044] Figure 5 This is a high-resolution transmission electron microscope image of the barrier layer and the channel layer obtained according to an embodiment of the method for preparing a high two-dimensional electron gas concentration transistor with cooperative regulation of polar superlattice according to the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0046] like Figure 1 As shown, the polar superlattice cooperatively regulated high two-dimensional electron gas concentration transistor of this embodiment includes, from bottom to top, a substrate, a superlattice stress regulation layer, a stress relaxation layer, a barrier layer and a channel layer.

[0047] The method for preparing a high two-dimensional electron gas concentration transistor with coordinated regulation of polar superlattice in this embodiment includes the following steps:

[0048] 1) Carbon-surfaced 4H-SiC double-polished four-inch wafers are used as substrates for crystal epitaxial growth templates and heat sink substrates. Their high thermal conductivity (490W / m·K) can quickly dissipate device operating heat and optimize device heat dissipation performance.

[0049] After H2 etching, atomic-level steps are formed on the substrate surface with a step height of 0.5 nm and a width of 150 nm. The substrate layer needs to be pretreated before epitaxy. The pretreatment temperature is 1050 ° C for 30 minutes and the background vacuum is ≤ 1×10 -10 Torr;

[0050] A three-step temperature gradient of 800°C → 950°C → 1050°C is used at the start of growth, which helps maintain the background vacuum of the MBE chamber while eliminating impurity molecules adsorbed on the substrate layer, such as water molecules and air molecules;

[0051] The lattice constant of 4H-SiC is and GaN lattice constant A 3.5% lattice mismatch is formed, so a GaN nucleation layer is required to alleviate the lattice mismatch between the substrate and the buffer layer and suppress the formation of threading dislocations;

[0052] The nucleation layer is grown at low temperature (500℃) to form an amorphous-nanocrystalline transition layer, and the dislocation density is reduced to 5×10 9 cm -2 ;

[0053] GaN was grown using periodic interruptions, with a 30-second pause every 5 minutes to promote surface growth and reconstruction. The growth conditions for the nucleation layer were: Ga source temperature 950°C, beam equivalent pressure (BEP) = 5×10 -7 Torr; high-purity nitrogen flow rate Flux = 1 sccm, and the nitrogen plasma RF source power is set to above 500 W to excite active nitrogen species and form a nucleation layer with a thickness of 200 nm;

[0054] GaN was grown on the nucleation layer under the following growth conditions: Ga source temperature 930°C, beam equivalent pressure BEP = 4×10 - 7Torr. High-purity nitrogen flow rate Flux = 1 sccm, nitrogen plasma RF source power is set to 400W, growth temperature is 680℃, continuous growth is adopted, thickness is 500nm, forming a buffer layer that can form a high-quality crystal template on the gallium nitride nucleation layer, providing a low defect density foundation for the subsequent superlattice layer; according to the Matthews-Blakeslee model, the critical thickness of the buffer layer h c for:

[0055]

[0056] Where b is the Burgers vector of the second material, generally b = 0.3189nm, f is the lattice mismatch, and the lattice constant of 4H-SiC is and the lattice constant of GaN To form a 3.5% lattice mismatch, f = 3.5% is generally selected; h is calculated c ≈1.2μm; therefore, the thickness of the GaN buffer layer should be no less than 1.2μm. The growth conditions of the GaN nucleation layer are: high temperature layer (750℃) and low temperature layer (650℃) grow alternately to form a dislocation blocking network, beam equivalent pressure (BEP) = 5×10 -7 Torr; high-purity nitrogen flow rate Flux = 1 sccm, nitrogen plasma RF source power set to 300W; V / III ratio dynamically controlled, gradually decreasing from an initial 2 to 0.8, promoting the transition from a three-dimensional growth mode to a two-dimensional growth mode;

[0057] 2) AlN and GaN are grown alternately on the substrate. The growth conditions are: Ga source temperature 930°C, beam equivalent pressure BEP = 4×10 -7 Torr; Al source temperature 1090℃, beam equivalent pressure BEP=6.7×10 - 8 Torr, high-purity nitrogen flow Flux = 1 sccm, nitrogen plasma RF source power is set to 400W, and growth temperature is 680℃; multiple cycles are grown to form a superlattice stress control layer. AlN and GaN have different lattice constants, resulting in lattice mismatch, which generates in-plane compressive stress; the magnitude of the compressive stress is controlled by adjusting the lattice mismatch; the compressive stress induced by the first material in a single cycle σ A Satisfy the following formula:

[0058]

[0059] Among them, E B is the elastic modulus of the second material, ν B is the Poisson's ratio of the second material, Δa is the lattice mismatch between the first material and the second material, aB is the lattice constant of the second material. In this embodiment, E B =300GPa,ν B =0.18, Δa=0.0077nm, To maintain a high in-plane compressive stress and reduce the interface roughness between the first and second materials, and to prevent mutual interference of stress fields within the multi-period superlattice, the compressive stress storage efficiency of the first material is ensured to be greater than 90% within a single period, and mutual interference of stress fields within the multi-period superlattice is prevented. Within a single period, the thicknesses of aluminum nitride and gallium nitride are 3 atomic layers and 7 atomic layers, respectively, for a total thickness of 50 nanometers.

[0060] 3) GaN was grown on the superlattice stress control layer under the following growth conditions: Ga source temperature 930°C, beam equivalent pressure BEP = 4×10 -7 Torr, high-purity nitrogen flow Flux = 1 sccm, nitrogen plasma RF source power is set to 400 W, growth temperature is 680 ° C, continuous growth is adopted, thickness is 150 nm, and a stress relaxation layer is formed. The stress relaxation layer releases the excess stress accumulated in the superlattice stress regulation layer through the dislocation bending mechanism. Most of the compressive stress of the superlattice stress regulation layer on the upper structure is shielded by the stress relaxation layer; the relaxation degree is controlled by adjusting the thickness of the stress relaxation layer; the relaxation degree R is related to the thickness t of the stress relaxation layer. B The relationship between them satisfies:

[0061]

[0062] Where k is the stress relaxation coefficient, k = 0.05; the thickness of the stress relaxation layer t B =150nm, R=92%, the stress relaxation layer shields most of the compressive stress of the superlattice stress regulation layer on the upper structure. The greater the relaxation degree, the smaller the high pressure stress, further regulating the compressive stress of the superlattice stress regulation layer; the stress relaxation layer reduces the compressive stress by relaxation, and separates the superlattice stress regulation layer from the barrier layer, preventing longitudinal leakage current and mutual interference between the energy bands of the superlattice stress regulation layer and the barrier layer;

[0063] 4) AlGaN was grown on the stress relaxation layer under the following growth conditions: Ga source temperature 930°C, beam equivalent pressure BEP = 4×10 -7 Torr; Al source temperature 1070℃, beam equivalent pressure BEP=2.7×10 -8 Torr; high-purity nitrogen flow rate Flux = 1 sccm, nitrogen plasma RF source power set to 400 W, growth temperature set to 700°C; AlGaN continuous growth with an aluminum content of 23% and a thickness of 10 nm was used to form a barrier layer;

[0064] 5) GaN is grown on the barrier layer under the following growth conditions: Ga source temperature 930°C, beam equivalent pressure BEP = 4×10 - 7 Torr; high-purity nitrogen flow rate Flux = 1 sccm, nitrogen plasma RF source power set to 400 W, growth temperature 680 ° C; continuous growth, thickness 10 nm, forming a channel layer; annealing and cooling, annealing temperature 710 ° C, hold time 30 minutes, heating and cooling rate 5 ° C / min;

[0065] 6) The barrier layer and the channel layer form a heterojunction. The lattice mismatch and polarization effect cause a large amount of uncompensated polarization charge to accumulate at the interface, inducing the formation of a high-concentration and high-mobility two-dimensional electron gas on the channel layer side. The channel layer acts as a low-defect, high-mobility conductive channel to achieve efficient electron transport. The two-dimensional electron gas is confined in a triangular potential well near the heterojunction interface between the barrier layer and the channel layer. The electrons can only move freely in the two-dimensional plane, which makes the electron mobility in the GaN channel layer reach 1600 cm 2 / (V·s) or more;

[0066] 7) The concentration of the two-dimensional electron gas is regulated by the barrier layer and the stress relaxation layer:

[0067] The concentration of the two-dimensional electron gas introduced by the barrier layer is related to the spontaneous polarization and piezoelectric polarization charge density of the barrier layer. The spontaneous polarization charge density is related to the composition of the group III element of the first material contained in the barrier layer, and the piezoelectric polarization charge density is related to the thickness of the barrier layer.

[0068] The compressive stress of the superlattice stress control layer generates a built-in electric field at the interface between the barrier layer and the channel layer, causing the band structure to bend. The band bending leads to a change in the two-dimensional electron gas concentration. The change in the two-dimensional electron gas concentration caused by the superlattice stress control layer is related to the period number and piezoelectric polarization charge density of the superlattice stress control layer, and the piezoelectric polarization charge density of the superlattice stress control layer is related to the compressive stress of the superlattice stress control layer.

[0069] By adjusting the thickness of the barrier layer and the composition of the group III element of the first material, as well as adjusting the period number and compressive stress of the superlattice stress control layer, the concentration of the two-dimensional electron gas is controlled to achieve an increase in the two-dimensional electron gas concentration without reducing the mobility;

[0070] The two-dimensional electron gas concentration is the total polarization charge density ρ total Satisfy the following formula:

[0071]

[0072] in, is the spontaneous polarization charge density of the barrier layer, is the piezoelectric polarization charge density of the barrier layer, is the piezoelectric polarization charge density introduced into the superlattice stress control layer, N is the number of periods of the superlattice stress control layer, is the piezoelectric polarization charge density introduced within a single period of the superlattice stress control layer.

[0073] The two-dimensional electron gas concentration of the GaN / AlN high-mobility transistor prepared in this embodiment is 1.6×10 13 cm -2 , the room temperature mobility is 1830cm 2 / (V·s).

[0074] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A method for preparing a high two-dimensional electron gas concentration transistor coordinated by polar superlattice, characterized in that: The preparation method comprises the following steps: 1) Providing a substrate, wherein the substrate is a semiconductor epitaxial substrate; 2) forming a superlattice stress regulation layer on the substrate, the superlattice stress regulation layer comprising a first material and a second material arranged alternately, the first material and the second material having the same number of layers, both of which are Group III-V elements, the Group V elements being the same but the Group III elements being different, and having different lattice constants; the difference in lattice constants between the first material and the second material results in a lattice mismatch, thereby generating in-plane compressive stress; and the magnitude of the compressive stress is regulated by adjusting the lattice mismatch; 3) forming a stress relaxation layer on the superlattice stress regulation layer, wherein the material of the stress relaxation layer is the same as the second material of the superlattice stress regulation layer; the stress relaxation layer releases excess stress accumulated in the superlattice stress regulation layer through a dislocation bending mechanism, and the compressive stress effect of the superlattice stress regulation layer on the upper structure is mostly shielded by the stress relaxation layer. The stress relaxation layer reduces the compressive stress through relaxation and separates the superlattice stress regulation layer from the barrier layer to prevent longitudinal leakage current and mutual interference between the energy bands of the superlattice stress regulation layer and the barrier layer; 4) forming a barrier layer on the stress relaxation layer, wherein the barrier layer is made of a ternary alloy of group III-V elements, the elements of which are consistent with those of the superlattice stress regulation layer, i.e., the two group III elements are the group III elements of the first material and the second material of the superlattice stress regulation layer respectively; 5) forming a channel layer on the barrier layer, wherein the material of the channel layer is the same as the second material of the superlattice stress regulation layer; 6) The barrier layer and the channel layer form a heterojunction. The lattice mismatch and polarization effect cause a large amount of uncompensated polarized charge to accumulate at the interface, inducing the formation of a high-concentration and high-mobility two-dimensional electron gas on the channel layer side. The channel layer acts as a low-defect, high-mobility conductive channel to achieve efficient electron transport. 7) The concentration of the two-dimensional electron gas is regulated by the barrier layer and the stress relaxation layer; The concentration of the two-dimensional electron gas introduced by the barrier layer is related to the spontaneous polarization and piezoelectric polarization charge density of the barrier layer. The spontaneous polarization charge density is related to the composition of the group III element of the first material contained in the barrier layer, and the piezoelectric polarization charge density is related to the thickness of the barrier layer. The compressive stress of the superlattice stress control layer generates a built-in electric field at the interface between the barrier layer and the channel layer, causing the band structure to bend. Band bending causes changes in the two-dimensional electron gas concentration; the changes in the two-dimensional electron gas concentration caused by the superlattice stress control layer are related to the period number and piezoelectric polarization charge density of the superlattice stress control layer, and the piezoelectric polarization charge density of the superlattice stress control layer is related to the compressive stress of the superlattice stress control layer; By adjusting the thickness of the barrier layer and the composition of the group III element of the first material, as well as adjusting the period number and compressive stress of the superlattice stress control layer, the concentration of the two-dimensional electron gas is regulated, thereby increasing the concentration of the two-dimensional electron gas without reducing the mobility.

2. The preparation method according to claim 1, wherein The method further includes a nucleation layer formed on the substrate layer, wherein the material of the nucleation layer is the same as the second material of the superlattice stress regulating layer.

3. The preparation method according to claim 2, wherein It also includes a buffer layer, which is formed on the nucleation layer. The material of the buffer layer is the same as the second material of the superlattice stress regulation layer.

4. The preparation method according to claim 1, wherein In step 2), the first material and the second material are nitride, oxide or arsenide.

5. The preparation method according to claim 1, wherein In step 3), the stress relaxation layer adjusts the compressive stress of the superlattice stress control layer on the upper structure. The greater the relaxation degree, the smaller the compressive stress, thereby further regulating the compressive stress of the superlattice stress control layer.

6. The preparation method according to claim 1, wherein In step 4), the composition of the group III element of the first material contained in the barrier layer is between 0.2 and 0.

3.

7. The preparation method according to claim 1, wherein In step 5), the thickness of the channel layer is 10 nm to 70 nm.

8. The preparation method according to claim 1, wherein In step 7), the two-dimensional electron gas concentration ρ total Satisfy the following formula: in, is the spontaneous polarization charge density of the barrier layer, is the piezoelectric polarization charge density of the barrier layer, is the piezoelectric polarization charge density introduced into the superlattice stress control layer, N is the number of periods of the superlattice stress control layer, is the piezoelectric polarization charge density introduced within a single period of the superlattice stress control layer.

9. A high two-dimensional electron gas concentration transistor coordinated by polar superlattice, characterized in that: The high two-dimensional electron gas concentration transistor comprises: a substrate, a superlattice stress regulation layer, a stress relaxation layer, a barrier layer and a channel layer; wherein the substrate is a semiconductor epitaxial substrate; a superlattice stress regulation layer is formed on the substrate, the superlattice stress regulation layer comprising a first material and a second material arranged alternately, the first material and the second material having the same number of layers, both of which are made of group III-V elements, the group V elements of the two materials being the same but the group III elements being different, and having different lattice constants; the different lattice constants of the first material and the second material result in a lattice mismatch, thereby generating an in-plane compressive stress; by regulating The whole lattice mismatch regulates the magnitude of the compressive stress; a stress relaxation layer is formed on the superlattice stress regulation layer, and the material of the stress relaxation layer is the same as the second material of the superlattice stress regulation layer; the stress relaxation layer releases the excess stress accumulated in the superlattice stress regulation layer through the dislocation bending mechanism, and the compressive stress effect of the superlattice stress regulation layer on the upper structure is mostly shielded by the stress relaxation layer; the relaxation degree is regulated by adjusting the thickness of the stress relaxation layer; a barrier layer is formed on the stress relaxation layer, and the material of the barrier layer is a ternary alloy of group III-V elements, and the elements are consistent with those of the superlattice stress regulation layer, that is, two group III elements. The elements are group III elements of the first material and the second material of the superlattice stress regulation layer respectively; a channel layer is formed on the barrier layer, and the material of the channel layer is the same as the second material of the superlattice stress regulation layer; the barrier layer and the channel layer form a heterojunction; the concentration of the two-dimensional electron gas is regulated by the barrier layer and the stress relaxation layer; the concentration of the two-dimensional electron gas introduced by the barrier layer is related to the spontaneous polarization and piezoelectric polarization charge density of the barrier layer, the spontaneous polarization charge density is related to the composition of the group III elements of the first material contained in the barrier layer, and the piezoelectric polarization charge density is related to the thickness of the barrier layer; the compressive stress of the superlattice stress regulation layer is in the barrier layer A built-in electric field is generated at the interface with the channel layer, causing the band structure to bend, and the band bending leads to a change in the two-dimensional electron gas concentration; the change in the two-dimensional electron gas concentration caused by the superlattice stress regulation layer is related to the period number and piezoelectric polarization charge density of the superlattice stress regulation layer, and the piezoelectric polarization charge density of the superlattice stress regulation layer is related to the compressive stress of the superlattice stress regulation layer; by adjusting the thickness of the barrier layer and the composition of the group III element of the first material contained therein, as well as adjusting the period number and compressive stress of the superlattice stress regulation layer, the two-dimensional electron gas concentration is regulated, thereby achieving an increase in the two-dimensional electron gas concentration without reducing the mobility.

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